1. Field of the Invention
This invention relates to a pressure measuring system which can strongly resist the effects of electromagnetic induction or the like which accompanies large current and high voltage.
2. Discussion of the Background
In the prior art system employing a pressure gauge of the distortion type, electrical cords for transferring signals are required. These electrical cords are subject to the influence of electromagnetic induction that accompany large currents and high voltages associated with power apparatus and power machines within the plant, and accordingly the output of the prior art system is subject to errors.
One known pressure measuring system which is relatively little affected by the influences of the electromagnetic induction, for example, utilizes optical fibers. In such a pressure measuring system, light from a light source is projected onto a pressure-receiving diaphragm mirror via an optical fiber. The reflected light from the mirror is then projected to photosensitive elements through an optical fiber provided for light reception. Received reflected light is then converted to an electrical signal, and pressure is measured based on the change in the reflected light due to deflection to the diaphragm mirror.
However, in the prior art system of this kind, use is made of an ordinary light source so that the amount of the received light varies due to the light source itself as well as due to vibrations of the optical fibers caused by external forces. Hence there is the drawback that these vibrations in the light reveal themselves as apparent variations in pressure. In addition, because of the absence of dust-preventive measures for the installations section of the diaphragm mirror, stains tend to appear on the diaphragm mirror due to attachment of dust or the like. There is then another drawback that the reduction in the amount of the reflected light due to stains also shows itself as an apparent reduction in the pressure. In particular, due to the fact that both the optical fiber coupled to the light source and the optical fiber receiving reflected light are given no tilt with respect to the normal to the reflecting surface, the amount of reflected light received by the optical fiber for light reception is small, and in fact the reflected amount of light is considerably reduced. Moreover, the reduction in the received light amount sets a limitation on the sensitivity of the measurement obtained.